In a flurry of hastily arranged mini-summits this week, Hollande will seek to turn expressions of support into concerted, sharp-end action before the rare moment of unity passes.

His prospects for success are mixed. The leaders of the US, Russia, Germany and Britain – whom Hollande will meet separately over four days – agree unreservedly about the necessity of eradicating Isis. All want a peace deal to end the Syrian civil war. But there is less agreement on how to do this.

Britain

David Cameron, who met Hollande in Paris on Monday morning, presented the easiest target for the diplomatic offensive. The prime minister is plainly embarrassed that Britain has not joined France in bombing Isis in northern Syria. So he offered the next best thing: French use of the British military airbase at Akrotiri in Cyprus, plus mid-air refuelling for French combat planes. And he vowed that if he has his way, the RAF will soon join the fight in Syria.

But even here, differences of emphasis persist. Cameron stressed the problem of foreign fighters returning to Europe. At last week’s G20 summit, he said Britain would host a conference to raise funds to stem the flow of Syrian refugees. These priorities reflect the British focus on immigration and security.

United States

Hollande faces a bigger challenge in Washington on Tuesday. Barack Obama is under growing pressure to do more in Syria from Republicans and his own side, including the Democrat presidential hopeful Hillary Clinton. European diplomats complain the US leader does not appreciate the severity of the twin terrorism and refugee crises facing Europe.

So far, Obama has resisted his critics. He shocked even his own supporters by calling Paris a “setback”. He is adamant that the US will not put boots on the ground in Syria, beyond the limited special forces units he authorised last month. So Hollande’s hopes of proactive US engagement in a global coalition may be disappointed. More US airstrikes, more arms to Syrian rebels, more drone attacks – plus condolences – may be the best he gets.